When designing a vehicle's interior, it's essential to know what different colors, instrument layouts and lighting options will look like at different times of day. Certain shades of black, for instance, can look almost gray in bright sunlight, while instruments that are clearly visible at night may be subject to glare during the day. Since 2006, engineers at the Ford Motor Company have been using something called the Visual Performance Evaluation Lab (VPEL) to determine what the insides of their vehicles will look like at any time of day, under varying amounts of cloud cover.

The VPEL consists of a domed chamber, which the vehicle is parked inside of. One end of a curved metal arm is attached to a center pivot at the top of the dome, while the other end follows the curve of the wall down to the floor, where it can be wheeled around the dome's perimeter. A cluster of four 1,500-watt daylight-temperature spotlights are mounted on the arm, and can be moved up or down its length. By swiveling the arm around the vehicle, and moving the lights up or down, any combination of sun direction and height can be simulated.

An array of floodlights in the ceiling provide additional fill light, to complete the illusion of natural daylight. Altogether, the VPEL's 270 lights use a total of 6,000 watts.

Settings can be adjusted to vary the intensity of the light, or to mimic different weather conditions. The artificial lighting of a showroom or of streetlights can likewise be simulated. Of course, the lights can also be completely turned off, to simulate night.

Previously, Ford engineers had to take their vehicles out on the road to make such observations, but it was a time-consuming approach, as early morning light could only be observed in the early morning, dusk lighting only at dusk, and so on. Not only does the VPEL let them create any type of light whenever they want it, but they state that it also allows them to start working on interiors earlier in the production process, before vehicles are roadworthy.

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